PNS Disorders

Question 1

Peripheral Nerve Structure

Answer 1

1. Endoneurium: delicate CT, surrounds each fibre, important in nerve fibre regeneration
2. Perineurium: surrounds bunches of axons + endoneurium sheath, nerve bundle now know as fascicle
3. Epineurium: dense CT, surrounds nerve, binds fascicles together

Question 2

Motor Unit

Answer 2

• Motor neuron + group of muscle fibres it innervates

- Smaller units recruited first, followed by larger units as muscle force increases

Question 3

UMN vs LMN

Answer 3

• UMN: cell bodies in the cerebral cortex that issue commands to LMNs (via the corticospinal/bulbar tract)
• LMN: cells bodies in the SC and BS that directly innervate skeletal muscle

Question 4

UMN Disorders

Answer 4

+++++

• Spasticity
• Overactive tendon reflexes
• Abnormal Babinski sign

Question 5

LMN Disorders

Answer 5

• Flaccidity
• Atrophy
• Fasciculations (muscle twitches)
• decreased muscle tone
• Loss of tendon reflexes

Question 6

Disease of Motor Unit

Answer 6

Classified by component affected:

1. Cell body: MND
2. Axon: peripheral neuropathies
3. Neuromusclar junction: myasthenia gravis, botulism

Question 7

Disease of the Axon Symptoms

Answer 7

Motor and sensory axons are bundles together, so both sensory and motor functions are affected

• • symptoms: numbness, tingling, burning, ‘pins and needles’ - caused by hyper excitability of nerves
• • symptoms: loss of sensation eg. pain and temp (more prominent distally - glove and stocking)

Question 8

Acute Disease of the Axon

Answer 8

Guillian-Barre Syndrome

• Often follows resp infection or infectious diarrheoa
• May be mild or so severe that ventilation is needed
• Autoimmune attack on peripheral nerves by circulating antibodies

Question 9

Pathogenesis of Guillian-Barre Syndrome

Answer 9

• Pathogens trigger humoral immune and autoimmune response through molecular mimicry
• Activates membrane attack complex
• Results in:
• > myelin detachment
• > disappearence of Na channels -> nerve cell dysfunction and symptoms